SAN DIEGO — Low serum vitamin D levels in the months preceding diagnosis may predict a high risk of premenopausal breast cancer, according to a prospective study led by researchers from the University of California, San Diego School of Medicine. 1

Drawing from 9 million blood serum specimens frozen by the DoD Serum Repository for routine disease surveillance, researchers looked at the blood levels of 1,200 healthy women, finding that women with low serum vitamin D levels during the three-month period just before diagnosis had approximately three times the risk of breast cancer as women in the highest vitamin D group.

Of the samples used, 600 were from women who later developed breast cancer and 600 were from women who remained healthy.

The study was published online by the journal Cancer Causes and Control.

“While the mechanisms by which vitamin D could prevent breast cancer are not fully understood, this study suggests that the association with low vitamin D in the blood is strongest late in the development of the cancer,” said principal investigator Cedric Garland, DrPH, FACE, of the Department of Family and Preventive Medicine at UC San Diego.

While analyses of vitamin D levels measured more than 90 days before diagnosis have not conclusively established a relationship between serum levels and risk of premenopausal breast cancer in the present cohort, the new study points to the possibility of a critical window for cancer prevention in the last three months preceding tumor diagnosis.

Garland noted that this is likely to be the point at which the tumor may be most actively recruiting blood vessels required for tumor growth. “Based on these data, further investigation of the role of vitamin D in reducing incidence of premenopausal breast cancer, particularly during the late phases of its development, is warranted,” he said.

He also cautioned that serum 25(OH)D be measured before substantially increasing a patient’s vitamin D intake.

“Reliance should not be placed on different forms of vitamin D, such as vitamin D2, and megadoses should be avoided except those ordered by a doctor for short-term use,” Garland added.